Nitrosoanisoles. Sensitive indicators of dimerisation criteria for C-nitrosoarenes.

A series of mono- and di-methyl substituted p-nitrosoanisoles was synthesis ed either by direct nitrosation of the anisoles with NO+HSO4- or by mild ox idation (H2O2-Mo catalyst) of the appropriate amines. The nature of these c ompounds in solution was established by, H-1 and C-13 NMR,spectroscopy. Var iable temperature H-1 dynamic NMR studies provided thermodynamic data for t he cases of dimer-monomer solution equilibria, and AG data for the restrict ed rotation of the N=O group in the monomers. Magnitudes of AG were in the range 28-41 kJ mol(-1) and Were shown to be sensitive predictors of self-di merisation tendencies of these compounds. This activation parameter, togeth er with the N-14,N-15 and O-17 chemical shifts of the N=O group, was shown to be a reliable predictor of self-dimerisation of nitroso compounds in gen eral.. The N=O bond length and the wavenumber of the IR-active N=O stretchi ng mode were found to be somewhat less reliable predictors of this behaviou r.